Custom targets were the origin of a number of issues with the mbed
tools, so it was decided that they need to be removed. This PR does just
that (and moves the "custom_targets" part of the config system tests
into a separate, per-test "targets.json" file to preserve the test
functionality).
PR #1974 added a new configuration parameter to K64F, which in turn made
some tests break, because they found an unexpected configuration
parameter. Fixed by defining a special target for the tests
(test_target) that can be used independently of the actual mbed targets.
Bogdan Marinescu
Vincent Coubard
Mihail Stoyanov